Wind Energy Resource Assessment and Turbine Energy Yield Using the Weibull Distribution

Abstract

The energy a wind turbine will produce at a site depends on how windy the site is and on how the turbine converts wind into power, and estimating it before installation is essential to deciding whether a site is worth developing. This study assesses the wind energy resource at a site and estimates the energy a turbine would yield there, combining a statistical description of the wind with the turbine's power curve. The distribution of wind speeds at the site was represented by the Weibull distribution, a two-parameter form widely used for this purpose, and the turbine's output was described by its power curve, which gives the power produced at each wind speed, zero below a cut-in speed, rising to a rated power, held constant to a cut-out speed, and zero beyond; the expected energy yield and the capacity factor were obtained by combining the two. The Weibull distribution represented the spread of wind speeds compactly through its two parameters, and combining it with the power curve gave the expected power and hence the annual energy yield and the capacity factor, the fraction of the turbine's rated output actually achieved. The yield depended strongly on the windiness of the site, a higher mean wind speed greatly increasing the energy because the power available in the wind rises steeply with speed, and on the match between the turbine's characteristics and the site's wind. The study shows that combining a Weibull description of the wind with the turbine power curve gives a sound estimate of energy yield for resource assessment, and it discusses the sensitivity of the yield to the wind resource and the turbine.

KEYWORDS: Wind energy, Resource assessment, Weibull distribution, Power curve, Capacity factor, Energy yield, Wind speed, Renewable energy, Turbine